Microelectronic devices, such as memory devices and microprocessors, often include a microelectronic die or “chip” that is packaged in a plastic, ceramic, or metal casing. The die generally has integrated circuitry and a plurality of bond-pads coupled to the integrated circuitry. For example, the integrated circuitry can include memory cells, processor circuits, interconnecting circuitry, and/or other components. The microelectronic device can also include an interposer substrate having a plurality of traces coupled to the bond-pads on the die and an array of ball-pads electrically connected to the traces. Each ball-pad typically carries a solder-ball to define a “ball-grid” array. In other applications, the microelectronic device can include a lead frame with metal leads instead of an interposer substrate. Packaged microelectronic devices with ball-grid array connections generally have lower profiles and higher pin counts than packages that use a lead frame.
Several different techniques have been developed for packaging microelectronic dies. The dies, for example, can be incorporated into individual protective packages, mounted with other components in a hybrid or multiple-chip module, or connected directly to a printed circuit board. In many packaging applications, the bond-pads on the die are coupled to a lead frame or a ball-grid array using wire bonds. After coupling the bond-pads to a lead frame or a ball-grid array, the dies are encased with a plastic, a ceramic, or another type of protective material.
The microelectronic package is subject to thermal cycling during bake-in, testing, and solder reflow processes. For example, solder reflow processes for surface mounting and through-hole mounting techniques are performed at approximately 220° C.; the packaged devices are then cooled. Microelectronic packages are also subject to thermal cycling during operation that can range from several degrees for a personal computer to several hundred degrees for extreme uses, such as in avionics.
One problem with packaged microelectronic devices is that thermal cycling induces stresses that can cause components to delaminate. The stresses are induced because the materials in a microelectronic package have different Coefficients of Thermal Expansion (“CTE”) so that they do not expand and contract the same amount during thermal cycling. As such, delamination often occurs at the interfaces between various components in the microelectronic package.